State Rep. Joaquín Castro speaks during the Librotraficante Banned Book Bash at the Guadalupe Theater.

State Rep. Joaquín Castro speaks during the Librotraficante Banned Book Bash at the Guadalupe Theater.

Photo: Robin Jerstad, For The Express-News

State Rep. Joaquín Castro speaks during the Librotraficante... Photo-3394368.48312 - San Antonio Express-News

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Julián or Joaquín?

Julián or Joaquín?

Photo: Tom Reel, San Antonio Express-News

Julián or Joaquín? Photo-3398907.48312 - San Antonio Express-News

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State Rep. Joaquín Castro (right) talks with his brother, former San Antonio Mayor Julián Castro as CPS announces OCI Solar Power as the choice to bring a 400 megawatt solar power plant to San Antonio at a LaVillita Assembly Hall event on January 11, 2012.

State Rep. Joaquín Castro (right) talks with his brother, former San Antonio Mayor Julián Castro as CPS announces OCI Solar Power as the choice to bring a 400 megawatt solar power plant to San Antonio at a

Former San Antonio Mayor Julián Castro addresses an audience at a luncheon for the National Association of Latino Elected and Appointed Officials (NALEO) conference at the Grand Hyatt on Thursday, June 23, 2011.

Former San Antonio Mayor Julián Castro addresses an audience at a luncheon for the National Association of Latino Elected and Appointed Officials (NALEO) conference at the Grand Hyatt on Thursday, June 23,

Former Mayor Julián Castro presents his annual State of the City address to the Greater San Antonio Chamber of Commerce on Friday, March 23, 2012.

Former Mayor Julián Castro presents his annual State of the City address to the Greater San Antonio Chamber of Commerce on Friday, March 23, 2012.

Photo: Helen L. Montoya, San Antonio Express-News

Former Mayor Julián Castro presents his annual State of the City... Photo-3394345.48312 - San Antonio Express-News

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Julián or Joaquín?

Julián or Joaquín?

Photo: Jennifer Whitney, For The Express-News

Julián or Joaquín? Photo-3394363.48312 - San Antonio Express-News

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State Rep. Joaquín Castro is handed the microphone by Vice Commander Walter Geraghty Jr. as he prepares to recognize Persian Gulf ware veterans and all vets during the American Legion Post 336 Monthly Meeting at Leon Valley Elementary School Cafeteria, Monday, March 21, 2012.

State Rep. Joaquín Castro is handed the microphone by Vice Commander Walter Geraghty Jr. as he prepares to recognize Persian Gulf ware veterans and all vets during the American Legion Post 336 Monthly Meeting